Vector control is a widely used technique in three phase converter topologies where power flow may be bidirectional (i.e., used as a rectifier or an inverter) due to its high performance characteristics. In vector control, two pulse width modulation (PWM) schemes are often used. One is a traditional sine/Δmodulation (sine/ΔPWM), and the other is space vector PWM (SVPWM). With the progress of digital control technology, SVPWM has drawn more interests since as it has an advantage of accommodating wider AC voltage ranges for a fixed DC bus voltage. Additionally, SVPWM may provide a reduced switching frequency for comparable ripple performance, thereby resulting in critical thermal benefits. Additionally, SVPWM can be implemented by employing either a hardware or software approach.
While generally, good current waveforms are not difficult to obtain, the application of SVPWM in products has been very limited due to its large common mode noise. In rectifier applications, this common mode noise causes serious electromagnetic interference (EMI) and stability problems for the converter. In motor drive applications, it could cause bearing damage due to common mode current. In the case of parallel operation of multiple converters, a circulation current, caused by the common mode voltage, could disturb the power train and sometimes even damage the converter devices. Although larger common mode filters will help reduce the noise, they are often limited by their size and cost penalties. Additionally, common mode filters merely attenuate the noise rather than resolve the source of the noise.
Accordingly, what is needed in the art is a more effective way to reduce common mode noise associated with three phase converters.